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XMP FAQ
In xmpdf: Edit 'XMP' Metadata and 'PDF' Bookmarks and Documentation Info
Table of Contents
- How do I adjust the automatic guessing of missing XMP tags?
- Which XMP tags have an active binding?
- How do I get or set XMP tags without an active binding?
- What XMP tags are used to display informaton on Google Images?
- Which tags should I use for Creative Commons license information?
- How do I embed XMP metadata in multiple languages?
- How do I enter in a "structured" tag?
- Is there an easy way to embed XMP metadata when using {knitr}?
- What are some helpful XMP external links?
How do I adjust the automatic guessing of missing XMP tags?
The auto_xmp active binding for xmp() objects is a character vector of XMP tags that if missing
{xmpdf} will try to automatically guess based on values of other XMP tags and the spdx_id active binding (SPDX License List Identifer).
When printing xmp() objects one can observe which XMP tags are guessed because they'll have a => on their left.
library("xmpdf")
x <- xmp(creator = "John Doe", date_created = "2023-02-10", spdx_id = "CC-BY-4.0")
print(x)
If you remove an XMP tag from auto_xmp then {xmpdf} will no longer try to guess it:
library("xmpdf")
x <- xmp(creator = "John Doe", date_created = "2023-02-10", spdx_id = "CC-BY-4.0")
x$auto_xmp <- base::setdiff(x$auto_xmp,
c("dc:rights", "photoshop:Credit"))
print(x)
Alternatively you could explicitly set a missing XMP tag (which then would no longer need to be guessed):
library("xmpdf")
x <- xmp(creator = "John Doe", date_created = "2023-02-10")
x$rights <- "© 2023 A Corporation. Some rights reserved."
print(x)
Which XMP tags have an active binding?
XMP tags with an active binding in xmp() objects will automatically be coerced into the right data type and are a little easier to get/set than XMP tags without an active binding. Here is a list of current active bindings provided by xmp() objects:
| Active Binding | XMP tag |
|---|---|
| alt_text | Iptc4xmpCore:AltTextAccessibility |
| attribution_name | cc:attributionName |
| attribution_url | cc:attributionURL |
| create_date | xmp:CreateDate |
| creator | dc:creator |
| creator_tool | xmp:CreatorTool |
| credit | photoshop:Credit |
| date_created | photoshop:DateCreated |
| description | dc:description |
| ext_description | Iptc4xmpCore:ExtDescrAccessibility |
| headline | photoshop:Headline |
| keywords | pdf:Keywords |
| license | cc:license |
| marked | xmpRights:Marked |
| modify_date | xmp:ModifyDate |
| more_permissions | cc:morePermissions |
| producer | pdf:Producer |
| rights | dc:rights |
| subject | dc:subject |
| title | dc:title |
| usage_terms | xmpRights:UsageTerms |
| web_statement | xmpRights:WebStatement |
How do I get or set XMP tags without an active binding?
If you want to set an XMP tag without an active binding you must use the xmp() objects set_item() method. To get an XMP without an active binding you must use the xmp() objects get_item() method. You may also use get_item() and set_item() for XMP tags with an active binding as well.
library("xmpdf")
x <- xmp()
x$set_item("dc:contributor", c("John Doe", "Jane Doe"))
x$get_item("dc:contributor")
Depending on the value type of the XMP tag you may need to manually coerce it to a special R class:
| XMP value type | R function to coerce |
|---|---|
| date | datetimeoffset::as_datetimeoffset() |
| lang-alt | xmpdf::as_lang_alt() |
library("datetimeoffset")
library("xmpdf")
transcript <- c(en = "An English Transcript",
fr = "Une transcription française") |>
as_lang_alt(default_lang = "en")
last_edited <- "2020-02-04T10:10:10" |>
as_datetimeoffset()
x <- xmp()
x$set_item("Iptc4xmpExt:Transcript", transcript)
x$set_item("Iptc4xmpExt:IPTCLastEdited", last_edited)
What XMP tags are used to display informaton on Google Images?
Google Images can show more details about an image when certain metadata is specified:
1) Structured data on the web page the image appears (takes priority over XMP tags if defined)
2) XMP tags embedded in the image
dc:creatorphotoshop:Creditdc:rightsxmpRights:WebStatement- the
Licensor URL subfield of plus:Licensor structured XMP tag
xmp() object's print(mode = "google_images") will tell what the Google Images XMP tags metadata would be:
library("xmpdf")
x <- xmp(attribution_url = "https://example.com/attribution",
creator = "John Doe",
description = "An image caption",
date_created = Sys.Date(),
spdx_id = "CC-BY-4.0")
print(x, mode = "google_images", xmp_only = TRUE)
Which tags should I use for Creative Commons license information?
Creative Commons recommends you specify the following XMP tags to indicate your license information:
dc:rightsxmpRight:MarkedxmpRights:WebStatementxmpRights:UsageTermscc:licensecc:morePermissionscc:attributionURLcc:attributionName
xmp() object's print(mode = "creative_commons") will tell what this XMP tags metadata would be:
library("xmpdf")
x <- xmp(attribution_url = "https://example.com/attribution",
creator = "John Doe",
description = "An image caption",
date_created = Sys.Date(),
spdx_id = "CC-BY-4.0")
print(x, mode = "creative_commons", xmp_only = TRUE)
How do I embed XMP metadata in multiple languages?
Although some XMP metadata tags must be a string in a single language but some XMP metadata tags support "language alternative aka "lang-alt" values which allow values for multiple languages to be specified:
Iptc4xmpCore:AltTextAccessibilitydc:descriptionIptc4xmpCore:ExtDescrAccessibilitydc:rightsdc:titlexmpRights:UsageTerms- Plus other XMP tags which will need to be manually coerced by
as_lang_alt() and set with the xmp() object's set_item() method
See ?as_lang_alt for more details but essentially create a character vector or list and name the entries with an RFC 3066 name tag.
library("xmpdf")
x <- xmp()
x$description <- "Description in only one default language"
x$title <- c(en = "An English Title",
fr = "Une titre française")
# XMP tags without an active binding must be manually coerced by `as_lang_alt`
transcript <- c(en = "An English Transcript",
fr = "Une transcription française") |>
as_lang_alt(default_lang = "en")
x$set_item("Iptc4xmpExt:Transcript", transcript)
How do I enter in a "structured" tag?
Currently {xmpdf} does not officially support entering in "struct" XMP tags (although it does support "lang-alt" tags and simple lists of basic XMP value types).
If necessary you'll need to use an external program such as exiftool (perhaps via {exiftoolr}) to embed structured XMP tags.
Is there an easy way to embed XMP metadata when using {knitr}?
{knitr} supports the chunk option fig.process which accepts a function to post-process figure files. The first argument should be a path to the figure file and may optionally accept an options argument which will receive a list of chunk options. It should return a (possibly new) path to be inserted in the output.
xmp() objects have a fig_process() method which return a function that can be used for this fig.process option to embed XMP metadat into images. Depending on the strings in its auto argument this function will also automatically map the following {knitr} chunk options to XMP tags:
fig.cap to dc:descriptionfig.scap to photoshop:Headlinefig.alt to Iptc4xmpCore:AltTextAccessibility
.. {r setup, echo=FALSE}
x <- xmpdf::xmp(creator = "John Doe",
date_created = "2023",
spdx_id = "CC-BY-4.0",
attribution_url = "https://example.com/attribution")
knitr::opts_chunk$set(fig.process = x$fig_process())
.. ..
What are some helpful XMP external links?
- IPTC Photo Metadata Standard (IPTC) is a popular XMP metadata standard for photos
- Quick guide to IPTC Photo Metadata on Google Images (IPTC) describes the subset of the IPTC Photo Metadata Standard used by Google Photos to list photo credits and license information
- xmp-docs (Adobe) describes some common XMP tags
- XMP (Creative Commons) describes a standard for using XMP to embed Creative Commons license information
- XMP tags (exiftool) is a fairly comprehensive list of XMP tags
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xmpdf documentation built on July 4, 2024, 9:08 a.m.
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Table of Contents
- How do I adjust the automatic guessing of missing XMP tags?
- Which XMP tags have an active binding?
- How do I get or set XMP tags without an active binding?
- What XMP tags are used to display informaton on Google Images?
- Which tags should I use for Creative Commons license information?
- How do I embed XMP metadata in multiple languages?
- How do I enter in a "structured" tag?
- Is there an easy way to embed XMP metadata when using {knitr}?
- What are some helpful XMP external links?
How do I adjust the automatic guessing of missing XMP tags?
The auto_xmp active binding for xmp() objects is a character vector of XMP tags that if missing
{xmpdf} will try to automatically guess based on values of other XMP tags and the spdx_id active binding (SPDX License List Identifer).
When printing xmp() objects one can observe which XMP tags are guessed because they'll have a => on their left.
library("xmpdf") x <- xmp(creator = "John Doe", date_created = "2023-02-10", spdx_id = "CC-BY-4.0") print(x)
If you remove an XMP tag from auto_xmp then {xmpdf} will no longer try to guess it:
library("xmpdf") x <- xmp(creator = "John Doe", date_created = "2023-02-10", spdx_id = "CC-BY-4.0") x$auto_xmp <- base::setdiff(x$auto_xmp, c("dc:rights", "photoshop:Credit")) print(x)
Alternatively you could explicitly set a missing XMP tag (which then would no longer need to be guessed):
library("xmpdf") x <- xmp(creator = "John Doe", date_created = "2023-02-10") x$rights <- "© 2023 A Corporation. Some rights reserved." print(x)
Which XMP tags have an active binding?
XMP tags with an active binding in xmp() objects will automatically be coerced into the right data type and are a little easier to get/set than XMP tags without an active binding. Here is a list of current active bindings provided by xmp() objects:
| Active Binding | XMP tag |
|---|---|
| alt_text | Iptc4xmpCore:AltTextAccessibility |
| attribution_name | cc:attributionName |
| attribution_url | cc:attributionURL |
| create_date | xmp:CreateDate |
| creator | dc:creator |
| creator_tool | xmp:CreatorTool |
| credit | photoshop:Credit |
| date_created | photoshop:DateCreated |
| description | dc:description |
| ext_description | Iptc4xmpCore:ExtDescrAccessibility |
| headline | photoshop:Headline |
| keywords | pdf:Keywords |
| license | cc:license |
| marked | xmpRights:Marked |
| modify_date | xmp:ModifyDate |
| more_permissions | cc:morePermissions |
| producer | pdf:Producer |
| rights | dc:rights |
| subject | dc:subject |
| title | dc:title |
| usage_terms | xmpRights:UsageTerms |
| web_statement | xmpRights:WebStatement |
How do I get or set XMP tags without an active binding?
If you want to set an XMP tag without an active binding you must use the xmp() objects set_item() method. To get an XMP without an active binding you must use the xmp() objects get_item() method. You may also use get_item() and set_item() for XMP tags with an active binding as well.
library("xmpdf") x <- xmp() x$set_item("dc:contributor", c("John Doe", "Jane Doe")) x$get_item("dc:contributor")
Depending on the value type of the XMP tag you may need to manually coerce it to a special R class:
| XMP value type | R function to coerce |
|---|---|
| date | datetimeoffset::as_datetimeoffset() |
| lang-alt | xmpdf::as_lang_alt() |
library("datetimeoffset") library("xmpdf") transcript <- c(en = "An English Transcript", fr = "Une transcription française") |> as_lang_alt(default_lang = "en") last_edited <- "2020-02-04T10:10:10" |> as_datetimeoffset() x <- xmp() x$set_item("Iptc4xmpExt:Transcript", transcript) x$set_item("Iptc4xmpExt:IPTCLastEdited", last_edited)
What XMP tags are used to display informaton on Google Images?
Google Images can show more details about an image when certain metadata is specified:
1) Structured data on the web page the image appears (takes priority over XMP tags if defined) 2) XMP tags embedded in the image
dc:creatorphotoshop:Creditdc:rightsxmpRights:WebStatement- the
Licensor URLsubfield ofplus:Licensorstructured XMP tag
xmp() object's print(mode = "google_images") will tell what the Google Images XMP tags metadata would be:
library("xmpdf") x <- xmp(attribution_url = "https://example.com/attribution", creator = "John Doe", description = "An image caption", date_created = Sys.Date(), spdx_id = "CC-BY-4.0") print(x, mode = "google_images", xmp_only = TRUE)
Which tags should I use for Creative Commons license information?
Creative Commons recommends you specify the following XMP tags to indicate your license information:
dc:rightsxmpRight:MarkedxmpRights:WebStatementxmpRights:UsageTermscc:licensecc:morePermissionscc:attributionURLcc:attributionName
xmp() object's print(mode = "creative_commons") will tell what this XMP tags metadata would be:
library("xmpdf") x <- xmp(attribution_url = "https://example.com/attribution", creator = "John Doe", description = "An image caption", date_created = Sys.Date(), spdx_id = "CC-BY-4.0") print(x, mode = "creative_commons", xmp_only = TRUE)
How do I embed XMP metadata in multiple languages?
Although some XMP metadata tags must be a string in a single language but some XMP metadata tags support "language alternative aka "lang-alt" values which allow values for multiple languages to be specified:
Iptc4xmpCore:AltTextAccessibilitydc:descriptionIptc4xmpCore:ExtDescrAccessibilitydc:rightsdc:titlexmpRights:UsageTerms- Plus other XMP tags which will need to be manually coerced by
as_lang_alt()and set with thexmp()object'sset_item()method
See ?as_lang_alt for more details but essentially create a character vector or list and name the entries with an RFC 3066 name tag.
library("xmpdf") x <- xmp() x$description <- "Description in only one default language" x$title <- c(en = "An English Title", fr = "Une titre française") # XMP tags without an active binding must be manually coerced by `as_lang_alt` transcript <- c(en = "An English Transcript", fr = "Une transcription française") |> as_lang_alt(default_lang = "en") x$set_item("Iptc4xmpExt:Transcript", transcript)
How do I enter in a "structured" tag?
Currently {xmpdf} does not officially support entering in "struct" XMP tags (although it does support "lang-alt" tags and simple lists of basic XMP value types).
If necessary you'll need to use an external program such as exiftool (perhaps via {exiftoolr}) to embed structured XMP tags.
Is there an easy way to embed XMP metadata when using {knitr}?
{knitr} supports the chunk option fig.process which accepts a function to post-process figure files. The first argument should be a path to the figure file and may optionally accept an options argument which will receive a list of chunk options. It should return a (possibly new) path to be inserted in the output.
xmp() objects have a fig_process() method which return a function that can be used for this fig.process option to embed XMP metadat into images. Depending on the strings in its auto argument this function will also automatically map the following {knitr} chunk options to XMP tags:
fig.captodc:descriptionfig.scaptophotoshop:Headlinefig.alttoIptc4xmpCore:AltTextAccessibility
.. {r setup, echo=FALSE} x <- xmpdf::xmp(creator = "John Doe", date_created = "2023", spdx_id = "CC-BY-4.0", attribution_url = "https://example.com/attribution") knitr::opts_chunk$set(fig.process = x$fig_process()) .. ..
What are some helpful XMP external links?
- IPTC Photo Metadata Standard (IPTC) is a popular XMP metadata standard for photos
- Quick guide to IPTC Photo Metadata on Google Images (IPTC) describes the subset of the IPTC Photo Metadata Standard used by Google Photos to list photo credits and license information
- xmp-docs (Adobe) describes some common XMP tags
- XMP (Creative Commons) describes a standard for using XMP to embed Creative Commons license information
- XMP tags (exiftool) is a fairly comprehensive list of XMP tags
Try the xmpdf package in your browser
Any scripts or data that you put into this service are public.
R Package Documentation
Browse R Packages
We want your feedback!
Note that we can't provide technical support on individual packages. You should contact the package authors for that.
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